569 HIGH-STRENGTH GYPSUM BASED ON β-HEMIHYDRATE GYPSUM BINDER Leonid Dvorkin, Vadim Zhitkovsky ABSTRACT The article substantiates the possibility of obtaining a high-strength gypsum binder of compressive strength after 2 hours of hardening in air-dry conditions of more than 10 MPa with the introduction of complex additives, including polyacrylate and polycarboxylate superplasticizer and lime. In order to achieve sufficient plasticity, an intensive method of mixing the gypsum paste is recommended. The kinetics of hardening of gypsum binder with complex additives was investigated by determining the strength, as well as changes in electrical resistivity and the speed of ultrasound transmission at different times of hardening. Experimental data have been obtained on the growth of the strength of gypsum binder with complex additives in time and the possibility of achieving in the dried state the strength of the hardened gypsum up to 25 - 26 MPa. Studies performed using X-ray phase and electron microscopic analysis have shown that the use of complex additives makes it possible to modify the structure of artificial gypsum stone and provide a denser arrangement of СаSO 4 ×2H 2 O crystals and a significantly lower intercrystalline porosity. Keywords: superplasticizers, lime, β-modification gypsum, polyfunctional modifier, high-strength gypsum, compressive strength. Received 07 October 2021 Accepted 30 January 2022 Journal of Chemical Technology and Metallurgy, 57, 3, 2022, 569-576 National University of Water and Environmental Engineering Ukraine, 33028, Rivne city, 11 Soborna St., NUWEE E-mail: [email protected] INTRODUCTION A key way to increase the strength of low-burning gypsum binders, consisting mainly of β-hemihydrate (β-СаSO 4 ×0.5Н 2 О) is to obtain an alpha modification of hemihydrate. However, the main method of obtaining α-hemihydrate - autoclave treatment - significantly complicates and increases the cost of binder technology and, therefore, is used very sparingly. The rather complex and energy-intensive technology of high- strength gypsum production in liquid media, which requires washing the product with hot water, dehydration in filters or centrifuges and drying, has not become widespread. Along with obtaining α-modification, a significant increase in the strength of gypsum binders can be achieved by using hard mixtures. However, the range of possible gypsum materials and products is significantly limited, press equipment is required [1 - 4]. New opportunities to increase the strength of gypsum binders have opened additives, which can significantly reduce the gypsum solution in gypsum mortars and concretes and increase their density [5 - 8]. In [6] it is proposed to use an additive of melamine- formaldehyde superplasticizer to improve the properties of gypsum. The greatest plasticizing effect was obtained with the introduction of 0.4 % - 0.8 % additive. At the same time, the water consumption of gypsum was reduced by 15 % - 20 %, and the strength increased by 30 % - 50 %. However, the proposed additive did not allow to obtain a high-strength gypsum binder. In [5] the effect of additives C-3, Melment and plasticizer based on polycarboxylate ether Stachement 2280 was analyzed by electron microscopic studies. In the system with the addition of polycarboxylate ether Stachement 2280 was achieved the higher degree of completion of the structure, and, accordingly, the maximum (8.9 MPa) strength of gypsum stone. In [9], the bases of obtaining modified gypsum binders of fine grinding by means of mechano-chemical
HIGH-STRENGTH GYPSUM BASED ON β-HEMIHYDRATE GYPSUM BINDER
Jun 20, 2023
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